A DC-to-DC converter is a device that accepts a DC input voltage and produces a DC output voltage of different voltage level than the input. There are two types of dc to dc converter circuits found in the CRT monitors.  
The "Buck step down converter” and the "Boost step up converter” circuit. About 80-90 % of the CRT Monitors are using the Boost step up converter circuit. The Buck step down converter circuit can buck a 160vdc into about 60 to 70 volts dc for the input to flyback transformer while the Boost step up transformer can boost the 45v volts  input to about 60 to 70v dc output. It depends on Monitor designs as what value the voltage would be going to the B+ pin of flyback transformer.

If anything goes wrong with these circuit, the Monitor might developed problems like no power, power blink, low power, power cycling, small width in display or even high voltage shutdown (only for the buck converter design). In addition, DC-to-DC converters are used to provide noise isolation, power bus regulation and etc.